Your sleep score describes the night that ended this morning, on a scale of 0 to 100. It is filed under the day you woke up, matching the convention Apple Health uses.
What goes into it
Four parts, weighted - duration counts most, stages least:
| Part | Measured against |
|---|---|
| Duration | A need of eight hours |
| Consistency | Your own recent bedtimes |
| Restfulness | Sleep efficiency and how often you woke |
| Stages | Your own usual deep and REM |
Duration carries the most weight because it is the thing wrist wearables measure best and the thing that matters most. You reach full marks a little under your full eight hours rather than needing to hit it exactly, and sleeping longer than your need is never penalised.
Consistency compares last night's bedtime with your median over the previous fortnight. There is a short grace period, then a gradual penalty for going to bed late. Going to bed early is treated much more gently, because an early night is rarely a problem.
Restfulness is mostly sleep efficiency, the share of time in bed you were asleep, plus a penalty for a fragmented night. The first few awakenings are free, since everybody surfaces briefly and it means nothing.
Stages is the smallest share, deliberately. See below.
Why deep and REM count for so little
Wrist and finger wearables estimate sleep stages, they do not measure them. Against a sleep lab, consumer devices identify deep sleep correctly something like half the time.
So stages are the smallest part of the score, well behind duration, and your deep and REM are compared only with your own typical levels, never with a target. You will not be told you are "short of the 15 to 25% you need", because that framing is not supportable on the underlying data and it makes people anxious about a number their device is partly guessing at.
If your deep sleep is well below your own usual, that is worth noticing. If it is below someone's idea of a healthy percentage, that is close to meaningless.
Light sleep is not scored at all.
What it needs before it works
- Stages need about five nights of your history before NOYU has a baseline to compare against.
- Consistency needs at least three prior nights.
- Duration and restfulness work from your very first night.
Until the rest catches up, your score is built from what is available and rebalanced accordingly.
Naps are excluded
Only your main sleep counts. Daytime naps are recorded, but do not feed the sleep score.
